Amorphous solar batteries having p-i-n junctions have been noted with keen interest for their extremely low production cost compared to single crystal solar batteries, and such amorphous solar batteries are lately considered the most hopeful of all types of solar batteries.
In the conventional amorphous solar batteries, the p-i-n junction (abbreviated as pin junction), that is, the junctions at the p/i and i/n interfaces had an abrupt step configuration. The solar batteries having such step type pin junctions have been produced mostly by using the glow-discharge plasma decomposition technique, and the P, i and n layers have been formed one after another in different film forming chambers separated from each other by means of valves, gas curtains, or forced gas discharges. Thus, for the production of the step type pin junction devices, it has been considered essential to keep the i layer free of any impurities.
However, according to the conventional separated three-chamber system, since the respective chambers for forming the p, i and n layers were separated from each other by valves or other means mentioned above, much time was required for the transfer of the workpieces from chamber to chamber, thus posing a problem with respect to productivity. Also, since substrate holders are moved successively through the three chambers, there would take place the re-release of dopant elements from the films adhering to the substrate holders in the course of said movement, resulting in a wide scatter in quality of the junction devices produced according to this method.
As a result of detailed studies for eliminating these drawbacks of the prior art, the present inventors have found that an amorphous semiconductor device having no distinct delineations of the p/i and i/n interfaces and having a freely controllable potential profile can be obtained without having any step type pin junctions where the dopant concentration is not changed abruptly stepwise but by introducing gradual changes in the dopant concentration, and such an amorphous semiconductor device (hereinafter referred to as a graded junction device) can function well as a solar battery. The present invention was achieved on the basis of this finding.
The first object of this invention, therefore, is to provide an amorphous semiconductor device which is easy to produce.
The second object of this invention is to provide a novel graded junction amorphous solar battery which involves no "junction" of the conventional conception.
The third object of this invention is to provide a method for producing the graded junction device with ease.
The fourth object of this invention is to provide an apparatus for producing the graded junction device.